Loud Knocking while Driving, Need Help Options

[86motoman]

I need help. I am currently riding my bicycle to work and school until I get this fixed. That is if I can get this fixed.

1972 Porsche 914 with a 1.7

It does not make noise with the clutch in. whether sitting still or coasting, it makes no noise at all with the clutch in.

It is loudest when accelerating or decelerating. The noise is more of a low knock while accelerating, and the noise is more of a higher knock while decelerating.

The knock gets a little quieter while applying little power from the engine. That is when on a flat surface just maintaining speed it quiets up a little.

Sometimes, not all the time, the knock goes away, just for a few seconds, after taking a corner.

I wiggled the axles. This novice came to the conclusion they are still there.

I felt all of the allen bolts holding the axles against the transmission side and wheel side. They all Appeared to be snug. I emphasize the word appeared.

Any help is appreciated.

[redshift]

Hmmm... good time to check transaxle for oil level..

I dunno. If you held the engine at 2000 rpm, how fast is the knocking?



M

[bd1308]

if you have completly sure that teh engine isnt the source of the sound--

one time, I was cheap and used regular gas in my 72 1.7.....uh, it made all kinds of racket. I very quickly went back to premium and havent looked back.

it sounded like a hammer against the case, softly.

b

[brp914]

does your oil pressure light work? At idle with the engine at full operating temp does the light come on? I'm kinda thinking worn bearings.

[r_towle]

with clutch in and no sound leads me to drivetrain.

Check
tranny fluid level
tighten all cv joint bolts
tighten the four motor mount bolts.
jack up car and wiggle check all bearings...could be a bad bearing.

I have some serious clunking from a bad bearing.

While the rear is jacked up, check for any play at all in the rear trailing arms...not only where the tire is attached, but where the trailing arm is attached to the car...use a long lever to wiggle and check for any play at all.

If the motor is making the noise, you could replicate it standing still clutch in by reving it really fast and then let off...if its a rod related issue, you will hear the same noise, though not as loud, when the car is decelerating from a very quick rev...

If it is loud at all revs, it could be valve related.

Rich

[86motoman]

I checked the tranny fluid. It was a little low, but it was plenty enough to operate without problems.

The oil level in the engine is fine.

I did just fill up with cheap gas. I usually use chevron. This time I used gas that has pinged in other vehicles I had.
It does sound like a hammer against the case, softly.

Cruising down the road about 30 mph roughly 2000 rpms the knock is not quite two a second.

There is no noise when the clutch is in and the engine is revved.

[Allan]

As I interpreted it, it sounds like it only knocks under load. I'm not to sure about the tranny/cv diagnosis.

[86motoman]

QUOTE (Headrage @ Jan 7 2006, 10:13 AM)

As I interpreted it, it sounds like it only knocks under load. I'm not to sure about the tranny/cv diagnosis.

I am starting to wonder the same thing. I guess that makes since that it would only detonate/ping underload. It sure sounds different, but I know sounds can be decieving.

I think I will go pick up some octane booster, and see what happens.

[bd1308]

dude, listen to me man. get some octane boost in that sucker very soon.

by cheap gas i'm talking about anything else besides 92 octane....

that compression (CR) is at a point, where, regular gas will tend to ping....

b

[86motoman]

I'll do it today before I drive it again. I hope that is the problem. That would be awesome! (IMG:http://www.914world.com/bbs2/html/emoticons/smilie_pokal.gif)

I'll keep you posted. Thank you guys!

[Rand]

If octane was the problem, shouldn't it just be pinging on acceleration? Why would that cause a knock on deceleration?

[dmenche914]

decel an acel noise, me is thinking drive train like CV's, you say the axles are there, but you need to check the free play in them to confirm if the CV's are the problem or not. grab the axles and rock them, more them in a twisting motion, and back and forth into and out of the CV's they should more in and out, but not with a lot of noise, and when twisting them there should be near zero free play.

[86motoman]

QUOTE (Rand @ Jan 7 2006, 11:24 AM)

If octane was the problem, shouldn't it just be pinging on acceleration? Why would that cause a knock on deceleration?

I am not sure if it would detonate on decel and accel. Something to consider is I haven't adjusted my valves for a long time, maybe 8000 to 10,000 miles. That maybe playing a role in it.

I am not ruling out a cv joint or wheel bearing or transmission failure. The knocking reminds me of when I broke a couple of teeth on a gm ring gear, but who knows. I thought it would be best to start with eliminating the easiest suspects, detonation.

To check the axles do I need to jack the wheel up? What I did is crawled under the car while it was being supported by the wheels. I pushed and pulled on the axle. I believe I went side by side as well, but I should recheck that.

[dmenche914]

i lift my 914 to check them, but then again my car is low. You want to be able to get both hands on them, and give them some good hard tugs, and twists to test them, if they wiggle in a twist or bind and are rough in either dierection , they need attention. (PS Be sure Car is safe before getting under, give the car several big pushes 10 times greater than you will on the axles. you want it to fall in a test push rather than when you push the axles will under the car. use caution.
Torn CV boots mean immediate attention before they destroy themselves, so don't ignore that either.
It is easist to get a check on R.P with car in gear, and one rear wheel off the ground (assuming CV's on that side already check good)
Wheel bearings need wheels off ground to be wiggle tested, very very slight wiggle is good (they can be tightened too much) but any more wiggle is bad. Front wheel bearings should be tested in both up down and right left directions while watching back side of wheel for tie rod movement, ball joint movent in addition to the wheel movement (wheel bearing)


Good luck, hopes it easy fix, update us.